It's funny that you mention that actually, the study mentions that they don't have many (or any?) men who were circumcised for religious reasons, they were all circumcised at a "doctor's estimate" which imo is weird language but I assume means it was for medical reasons.
Looks like they try to control for a lot of other factors, but I feel a bit weird about an article studying circumcision but not featuring those circumcised for the predominant reason that men are circumcised worldwide.
A different way to frame this would be "men who were circumcised specifically for medical reasons tend to have bad sex lives" which imo is a lot less surprising?
In some countries, non-religious "cultural" circumcision is very common (eg 75% of males in the US [0]). Relatively few cases will be for a medical reason (something like phimosis). Parents in most "secular circumcision" cultures base their circumcision decision primarily on social concerns, rather than medical concerns; the strongest predictor for the decision a couple will make is whether the father is circumcised or not[1]. So your point about religious circumcision being the most common is true worldwide (2/3 of circumcisions are for Muslim men[2]), but there are countries where this is significantly less of a factor.
Looks like they try to control for a lot of other factors, but I feel a bit weird about an article studying circumcision but not featuring those circumcised for the predominant reason that men are circumcised worldwide.
A different way to frame this would be "men who were circumcised specifically for medical reasons tend to have bad sex lives" which imo is a lot less surprising?